A typical ribbon cable assembly includes a portion of ribbon cable and a connector fastened at each end. The portion of ribbon cable is generally flat and thin, and includes multiple wire segments which extend in a parallel. Such a ribbon cable assembly can provide many electrical connections between a pair of electronic components (e.g., between a disk drive and a disk drive controller) in a well-organized and efficient manner.
Typically, each wire segment (or simply wire) of the ribbon cable portion includes a conductor and insulation which surrounds that conductor. In some ribbon cables, the conductor of each wire is a single solid strand. In other ribbon cables, the conductor of each wire includes multiple strands (e.g., seven) which are wound in a helix.
Each connector of the ribbon cable assembly typically includes a connector housing, and multiple metallic wire terminals which connect with the wire segments of the ribbon cable portion and which are held in place by the connector housing. The terminals are typically arranged in one or more rows.
Some terminals are configured to form insulation displacement connections (IDCs) with ribbon cable wires. One conventional IDC terminal includes a pair of metal tines at one end and a pin at the other end. The pair of tines define a rectangular-shaped slot, i.e., a slot having parallel edges, for receiving a wire. The comers of the slot (i.e., where the tines attach to the remaining portion of the IDC terminal) are typically coined (rather than sharply cut at 90 degrees) in order to prevent the tines from breaking off and to avoid creating stamping burrs that could sever the wire. When a wire inserts into the rectangular-shaped slot, the tines pierces the insulation around the wire in order to expose the conductor. As the wire further inserts into the rectangular-shaped slot, the tines push away some of the insulation and make direct contact with the conductor (e.g., metal-to-metal). The displaced insulation provides mechanical support to interference fit the wire within the rectangular-shaped slot. Furthermore, the tines provide a squeezing force that holds the wire within the rectangular-shaped slot.
It should be understood that the force provided by the tines against the wire gradually increases as the wire moves further into the rectangular-shaped slot. Although the force provided by the tines is greatest at their attachment points and weakest at the distal ends of the tines, final placement of the wire within the IDC terminal can occur anywhere within the slot. Manufacturers typically try to avoid placement of the wire at the bottom of the slot since such placement would risk inadvertently cutting the wire because the tines are rigid and no longer behave elastically at that point.
Automated machinery can install ribbon cable portions onto the connectors. In one approach, an arm presses (or stamps) the end of a ribbon cable portion onto a row of IDC terminals of a connector. As mentioned above, as each wire inserts into a corresponding IDC terminal, the tines of that terminal cut away insulation on that wire and contact the conductor of that wire. The pair of tines provide a squeezing force in order to hold the wire and provide an electrical pathway between the terminal and the wire. In some situations, the aggregate retention force between the IDC terminals and the ribbon cable wires is sufficient to retain the portion of ribbon cable within the connector. In other situations, the connectors further include a strain relief member (e.g., a clamp) that physically fastens to the portion of ribbon cable to prevent the ribbon cable portion from disconnecting from the connector.
Unfortunately, there are deficiencies to the above-described conventional ribbon cable assembly. In particular, the amount of electrical connectivity between a ribbon cable wire and its corresponding IDC terminal can vary (e.g., can differ for a particular wire over time, can differ from wire to wire, etc.).
For example, suppose that the conductor of a wire installed within an IDC terminal includes a bundle of strands which are twisted into a helix. Immediately after installation of the wire within the IDC terminal, the end of the conductor (i.e., the wire tail) may still retain much of its helix shape and make adequate electrical contact with the IDC terminal. However, over time subtle movements of the wire (e.g., due to normal handling and flexing of the ribbon cable assembly, vibration from neighboring equipment, changes due to temperature cycles/variations, etc.) can cause the strands of the wire to unravel. That is, some strands may stray from the bundle resulting in a fragmentation or loss of material in the main wire bundle at the contact area. Such separations reduce both the mechanical compression and electrical contact area. In this situation, there is less pressure between the remaining bundle and the tines thus lowering electrical connectivity between the wire and the IDC terminal. In some situations, the bundle may completely unravel from its helix shape leaving the wire with minimal or no electrical contact with the IDC terminal.
As another example, suppose that the conductor of a wire installed within an IDC terminal includes a single solid strand. Since the slot is rectangular in shape, the single solid strand contacts the IDC terminal in exactly two places, i.e., one side of the solid strand contacts one tine, and the other side of the solid strand contacts the other tine. Over time, the tines may dig into and deform the solid strand so that pressure between the tines and the solid strand decreases thus lowering electrical connectivity. Also, in some situations, a portion of the displaced insulation may work its way between the conductor and a tine, and thus interfere with one of the two contact points thus reducing electrical connectivity.
Such lowered electrical connectivity between the conductor and the IDC terminal can result in unreliable electrical pathways between electronic components which communicate through the ribbon cable assembly. In some situations, such pathways could provide intermittent electrical connections resulting in corrupted or lost data, excessive read or write errors (i.e., signal errors) requiring repeated read and write operations or, even worse, a failed connection that prevents the components from properly communicating all together.
In contrast to the above-described conventional ribbon cable assembly, the invention is directed to techniques for forming an insulation displacement connection using a terminal that defines wire positioners which can locate a wire within the terminal. The wire positioners facilitate wire retention and improve electrical connectivity thus providing a reliable electrical pathway between the wire and the terminal.
One arrangement of the invention is directed to a ribbon cable assembly which includes a segment of ribbon cable having first and second ends, a first IDC connector mounted to the first end of the ribbon cable segment, and a second IDC connector mounted to the second end of the ribbon cable segment. Each connector includes a connector housing, and a set of terminals supported by the connector housing. Each terminal has a base portion (e.g., a pin, a pad, etc.) for coupling to an external device, and a cable attachment portion which is unitary with the base portion of that terminal. The cable attachment portion of each terminal defines (i) a slot that receives a wire, and (ii) wire positioners that position the wire within the slot when the slot receives the wire. The wire positioners can position the wire such that it is held in an optimal location within the slot, i.e., a xe2x80x9csweet spotxe2x80x9d of the terminal for improved electrical connectivity.
In one arrangement, the cable attachment portion of each terminal includes a pair of jaws. Each wire positioner (e.g., a metallic bump) defined by the cable attachment portion of that terminal extends from a central region of a jaw toward a midline of the slot. Accordingly, the wire positioners can make electrical contact with the conductor of the wire to improve electrical connectivity. For example, if the conductor is a single solid strand, the wire positioners can provide additional points of contact with the conductor for better electrical connection (e.g., four points of contact rather than two points of contact as in the earlier-described conventional approach).
In one arrangement, the cable attachment portion of each terminal is configured to retain a wire having multiple strands (e.g., seven strands of 38 AWG wire), each strand having a diameter N (e.g., 0.00397 inches). In this arrangement, the cable attachment portion of each terminal preferably defines a gap between the wire positioners that is substantially half of the diameter N. Accordingly, strands of the wire will be unable to pass through the wire positioners and thus unable to stray from the bundle of strands further into the slot. As a result, the terminal constrains the bundle and sustains reliable electrical contact with the wire.
In one arrangement, the cable attachment portion of each terminal defines a substantially circular opening at a centrally disposed end of the slot defined by the cable attachment portion of that terminal. The substantially circular opening preferably has a diameter which is greater than a maximum width of the slot defined by the cable attachment portion of that terminal. Accordingly, parts (e.g., jaws) of the cable attachment portion can hinge at the circular opening. The hinging operation of the cable attachment portion, in combination with the operation of the wire positioners to precisely locate the wire, provides more consistent wire retention results (e.g., consistent pressure on the conductor) vis-a-vis the above-described conventional IDC terminal which provides a force which increases as the wire moves further down and into the slot and thus varies depending on how much the wire drifts (e.g., over time) within the slot of the conventional IDC terminal.
In one arrangement, the cable attachment portion of each terminal includes a pair of jaws that defines a portion of the slot such that the width of that portion of the slot narrows in a direction from a central location of the cable attachment portion toward an end of the cable attachment portion. Accordingly, the wire is prevented from moving (e.g., creeping) back up the slot. Additionally, if the wire includes a multi-stranded conductor, individual strands are constrained rather than allowed to unravel in a direction back up the slot thus preserving the wire bundle and sustaining the pressure between the wire bundle and the cable attachment portion of the terminal.
In one arrangement, ribbon cable assembly further includes a high-conductive metallic coating (e.g., gold, bronze, tin, lead, etc.) disposed over portions of the cable attachment portion of each terminal which define the wire positioners. The coating can improve electrical conductivity, prevent corrosion, etc. The location and amount of the coating can be controlled to avoid wasting the coating material over the entire terminal, i.e., to avoid placing the coating over terminal locations that are not intended for contact with the wire conductor.
The features of the invention, as described above, may be employed in connection systems, devices and methods and other computer-related components such as those provided by EMC Corporation of Hopkinton, Mass.